Project Summary Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor involved in various cellular biochemical reactions and contributes to the regulation of Ca2+ signaling, chromatin structure, DNA repair and lifespan. To date, how eukaryote cells transport and utilize NAD+ precursors as well as the signaling pathways that regulate NAD+ homeostasis remain unclear. Studying NAD+ homeostasis is also complicated by the complex and dynamic flexibility of precursors cells use to generate NAD+. Nicotinamide riboside (NR) and nicotinamide (NAM) are key pyridine metabolites that play important roles in maintaining NAD+ pools as well as calorie restriction (CR)-induced lifespan. To further understand the mechanisms of homeostasis, we have established specific genetic screen systems to identify yeast mutants with altered NAD+ metabolism. The current proposal builds on our recent studies of these mutants and the interplay between components in NR/NAM/NAD+ metabolism and longevity- related nutrient signaling pathways. The long-term goal is to understand the mechanisms by which cells maintain NAD+ homeostasis in response to changes in growth conditions. The major hypothesis is that NAD+ homeostasis is modulated by nutrient-sensing signaling pathways, which plays important roles in determining cell fitness and survival. The specific aims of the projects are: Aim 1) To study how NAD+ precursor assimilation factors regulate NAD+ homeostasis, Aim 2) To study the cross-regulation of NAD+ homeostasis and nutrient sensing pathways, and Aim 3) To Identify and study novel NAD+ homeostasis factors in the NA/NAM salvage pathway. This supplement request is made jointly by: Dr. Su-Ju Lin: GM102297 ?Understanding the regulation of NAD+ homeostasis signaling? Program Officer Dr. Stefan Maas; and Dr. Wolf Heyer GM58015 ?Recombinational Mechanisms of DNA Repair? Program Officer Dr. Kristine Willis. This request is for an FPLC protein purification system that is essential for the research program of Dr. Heyer and will greatly accelerate the research by Dr. Lin. The PIs developed a specific user plan (Lin 1/3, Heyer 2/3) and the budget accordingly. The total request to NIGMS by the two investigators is $72,934. The institutional commitment amounts to $24,000 to match the total cost of $96,934 indicated in the quote by the vendor.